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I added the check, modified the tests and removed all instances of "-> ()" that were already there.
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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix#15925 (github issue number if applicable).
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- [X] There are tests for these changes
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Source-Repo: https://github.com/servo/servo
Source-Revision: a6f89c503671726bcb0407cd84c380f3af4a7916
72a4fc3bbf